• Journal of the Korean Society of Propulsion Engineers
• /
• v.20 no.2
• /
• pp.75-85
• /
• 2016

A pyrotechnic system consisting of donor/acceptor pair separated by a gap relies on shock attenuation characteristics of the gap material and shock sensitivity of the donor and acceptor charges. Despite of its common use, numerical study of such pyrotechnic train configuration is seldom reported because proper modeling of the full process requires precise capturing of the shock wave attenuation in the gap prior to triggering a full detonation of high explosive and accurate description of the high strain rate dynamics of the explosively loaded inert confinements. We apply a Eulerian level-set based multimaterial hydrocode with reactive flow models for pentolite donor and heavily aluminized RDX as acceptor charge. The complex shock interaction, critical gap thickness, acoustic impedance, and go/no-go characteristics of the gap test are quantitatively investigated.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.10
• /
• pp.2686-2697
• /
• 1994

When a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel, which causes an impulsive noise. In order to estimate the magnitudes of the noises and to effectively minimize them, the characteristics of the compression wave propagating in a tunnel must be understood. In the present paper, the experimental and analytical investigations on the attenuation and distortion of the propagating compression waves were carried out using a model tunnel. This facility is a kind of open-ended shock tube with a fast-opening gate valve instead of a general diaphragm. One-dimensional flow model employed in the present study could appropriately predict the strength of the compression wave, Mach number and flow velocity induced by the compression wave. The experimental results show that the strength of a compression wave decreases with the distance from the tunnel entrance. The decreasing rate of the wave strength and pressure gradient in the wave is strongly dependent on the strength of the initial compression wave at the tunnel entrance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.147-152
• /
• 2006

This paper presents the dynamic characteristics of MR impact damper for vehicle collision system. Various types of mechanism have been proposed for reduce transmitted force to vehicle chassis and finally protect occupants from injury. In the case of frontal collision, the bumper make main role of isolation material for collision attenuation. In this study, proposed bumper system composed of MR impact damper and structures. The MR impact damper is to adopted MR fluid which has reversible properties with applied magnetic field. MR fluid operates under flow mode with Bingham flow and bellows is used for generation of fluid flow. Mathematical model of MR impact damper incorporated with MR fluid is established. Field dependent damping force is investigated with time and frequency domain. The MR impact damper is then incorporated with vehicle crash system. The governing equation of motion of vehicle model is formulated considering occupant model. Dynamic characteristics of vehicle collision system investigated with computer simulation.

• Wind and Structures
• /
• v.19 no.4
• /
• pp.389-404
• /
• 2014

The flow characteristics of a circular cylinder surrounded by an outer permeable cylinder were experimentally investigated using Particle Image Velocimetry Technique in deep water flow. In order to consider the effects of diameter and porosity of the outer cylinder on flow structures of the inner cylinder, five different outer cylinder diameters (D=37.5, 52.5, 60, 75 and 90 mm) and eight different porosities (${\beta}$=0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85) were selected. During the experiments, the diameter of inner cylinder was kept constant as d=30 mm. The depth-averaged free-stream velocity was adjusted as U=0.156 m/s, which corresponds to the Reynolds number of Re=5000 based on the inner cylinder diameter. It has been concluded that both the outer permeable cylinder diameter and the porosity have important influences on the attenuation of vortex shedding in the wake region. The presence of outer permeable cylinder decreases the magnitude of Reynolds shear stress and turbulent kinetic energy compared to the bare cylinder case. Moreover, the spectral analysis of vortex shedding frequency has revealed that the dominant frequency of vortex shedding downstream of the cylinder arrangement also reduces substantially due to the weakened Karman shear layer instability.

• Journal of Wetlands Research
• /
• v.14 no.4
• /
• pp.489-502
• /
• 2012

Biogeochemical processes in groundwater-stream water mixing zone are recently of great interest because biodegradation and natural attenuation of aquatic contaminants may occur through the processes. The objectives of this study are to investigate the hydrologic and biogeochemical processes at the groundwater-stream water mixing zone through which surface water-driven nitrate may be naturally attenuated, and to examine the effect of the vertical flow exchange flux on biogeochemical processes using correlation analysis. To examine the direction of vertical water flow in the zone, vertical hydraulic gradients were measured at several depths using mini-piezometers. Microbial populations in soil samples of the zone were also analyzed by means of the polymerase chain reaction (PCR) and Cloning methods. In addition, partial correlations among vertical flow exchange, nitrate concentration and microbial activity was investigated to examine their mutual interaction. The results showed the significant interaction among the three parameters, resulting in natural attenuation of nitrate. This study showed an example of the biogeochemical fuction of groundwater-stream water mixing zone, which can be predictable from the examination of the interaction among microbial activities, concentration of contamination and vertical flow exchange flux. temperature show a significant difference in adjacent streambed, Also, the results shows that distribution of temperature was more affected by groundwater direction than intensity of flux.

• Journal of Environmental Policy
• /
• v.9 no.1
• /
• pp.83-107
• /
• 2010

Urbanized environments are constructed to estimate peak flow and cost savings in response to possible BMP allocation at a watershed scale. The main goal is to explore the proper allocation of sub-watershed level BMPs for peak flow attenuation at a watershed scale. Since several individual site scale BMPs work as a form of aggregated BMPs at a sub-watershed scale, it is a question as to how to properly allocate the sub-watershed level BMPs at a watershed scale. The Hydrological Simulation Program-FORTRAN (HSPF) is set up for a hypothetically urbanized watershed. A peak flow is determined to be the primary variable of interest and targeted to characterize the spatial distribution of aggregated BMPs. Construction cost of a regional pond forms the basis of the economic valuation. The results indicate that when total size of BMPs is constant in the entire watershed, (1) it is most effective to have aggregated BMPs in some upper sub-watersheds while the BMPs in either the mainstem sub-watershed or a single sub-watershed are the least effective choices for peak flow attenuation at a watershed scale; (2) savings exist between allocation differences and reduced peak flow increases cost savings. The largest saving is found in the strategy of aggregated BMPs in some upper sub-watersheds. These findings, however, call for follow-up site specific case studies revisiting the watershed scale impacts of BMP allocation. Then, it will be argued that location and extent of decentralization are considerable policy variables for an alternative stormwater management policy at a watershed scale.

• Geomechanics and Engineering
• /
• v.23 no.4
• /
• pp.327-338
• /
• 2020

The role of precise prediction of subsurface fluids and discrimination among them cannot be ignored in reservoir characterization and petroleum prospecting. A suitable rock physics model should be build for the extraction of valuable information form seismic data. The main intent of current work is to present a rock physics model to analyze the characteristics of seismic wave propagating through a cracked porous rock saturated by a three phase fluid. Furthermore, the influence on wave characteristics due to variation in saturation of water, oil and gas were also analyzed for oil and water as wet cases. With this approach the objective to explore wave attenuation and dispersion due to wave induce fluid flow (WIFF) at seismic and sub-seismic frequencies can be precisely achieved. We accomplished our proposed approach by using BISQ equations and by applying appropriate boundary conditions to incorporate heterogeneity due to saturation of three immiscible fluids forming a layered system. To authenticate the proposed methodology, we compared our results with White's mesoscopic theory and with the results obtained by using Biot's poroelastic relations. The outcomes reveals that, at low frequencies seismic wave characteristics are in good agreement with White's mesoscopic theory, however a slight increase in attenuation at seismic frequencies is because of the squirt flow. Moreover, our work crop up as a practical tool for the development of rock physical theories with the intention to identify and estimate properties of different fluids from seismic data.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2004.05a
• /
• pp.257-262
• /
• 2004

A series of preliminary model tests are performed to find out the wave attenuating effect of the pneumatic breakwater of environment friendly type, which is a bubble screen generated by releasing compressed air from a submerged multiple parallel manifold Rising bubbles induce vertical current, which produces horizontal currents flowing away from the bubble-screen area in both directions. Near bottom, the corresponding currents flow toward the bubble screen, thus completing the circulation pattern. The surface current moving against the direction of wave propagation causes some attenuation of the waves. It becomes more effective as the relative depth (d/ L) increases (short-period waves in deep water). With the same air-discharge, the multiple parallel manifold can be more effective for the attenuation of longer waves through optimum arrangement of manifold number. installation depth, manifold gap, etc. The pneumatic breakwater will give a wide utilization as a device for protecting harbor facilities and as a simple, mobile breakwater.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.8
• /
• pp.1972-1981
• /
• 1995

As a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel, which causes an impulsive noise. The impulsive noise is closely related to the pressure gradient of the compression wave propagating the tunnel. In order to investigate the characteristics of the compression waves, in the present study an experiment was made using a shock tube. The results show that the strength of a compression wave decreases with the distance from the tunnel entrance and the nonlinear effect of compression wave appears to be significant if strength of the initial compression wave is greater than 7 kPa. Furthermore if the wave pattern is known, attenuation of the compression wave propagating in a tunnel can be reasonably predicted by a theoretical equation considering viscous action and heat transfer in boundary layer.

• The Journal of the Acoustical Society of Korea
• /
• v.29 no.1E
• /
• pp.38-44
• /
• 2010

This paper is based on our comments and proposed amendments to the documents, Annex A, Phantom for determining Maximum Depth of Penetration, and Annex B, Local Dynamic Range Using Acoustical Test Objects 87/400/CDV. IEC 61391-2 Ed. 1.0 200X, prepared by IEC technical Committee 87; Ultrasonics. The documents are concerned with the influence of microstructure of reference target material on the ultrasonic backscattering. Previous works on the attenuation due to backreflection and backscattering of reference target materials are reviewed. The drawback to the use of ungraded stainless steel and metallic materials without microstructural data such as, crystal structure, basic acoustic data of sound velocity and attenuation, grain size, roughness and elastic constants has been discussed. The analysis suggested that the insightful conclusion can be made by differentiating the influence arising from target size and microstructure on the backscattering measurements. The microstructural parameters are associated with physical, geometrical, acoustical and mechanical origins of variation with frequency. Further clarification of such a diverse source mechanisms for ultrasonic backscattering would make the target material and its application for medical diagnosis and therapy simpler and more reliable.